The present invention is generally directed to toner compositions, and more specifically to encapsulated toner compositions and processes thereof. In one embodiment, the present invention is related to processes for the continuous preparation of encapsulated toner compositions comprised of core components such as, for example, polymer resins, and colorants comprised of magnetic pigments, dyes, color pigments or mixtures thereof, and thereover a polymeric shell. Another embodiment of the present invention relates to a process for the continuous in situ preparation of heat fusible, or cold pressure fixable encapsulated toners comprised of a core containing a polymer resin, or plurality of polymer resins and magnetic pigment particlesm such as iron oxides or magnetites, encapsulated within a polymeric shell, such as a polyurethane, a polyester, a polyurea, and other known shell polymers. The encapsulated toners obtained with the processes of the present invention in embodiments possess a number of advantages including narrow particle size distribution, cold pressure fixability, low heat fusibility, high image fix, excellent powder flow characteristics, excellent surface release properties, and excellent toner shelf stability.
It is known that encapsulated toner can be prepared by a batch process. However, the batch process has several drawbacks, or disadvantages. For example, the processing down times can be extensive, for example from about 3 to about 6 hours, and hence volume/time yield can be relatively low, for example from about 2 to 4 times lower, compared with the continuous process of the present invention in embodiments; apparatus changeover and periodic addition of materials is needed, which not only increases the operating cost but also can cause product quality variation (batch-to-batch variation); and with low volume/time yield larger equipment, 2 to 4 times larger than continuous process equipment, is needed to achieve the same production volume, and this equipment may cause undesirable scalability problems and can increase costs. The equipment scaleup problem is particularly important because of the geometric dependence of the particle formation step and the unavailability of a manufacturing size homogenizer. These and other disadvantages are avoided, or minimized with the processes of the present invention.
Advantages associated with the continuous process of the present invention in embodiments includes high volume/time yields, such as 2 to 4 times higher than that obtained by batch process, no changeover of equipment, operation shutdown can be avoided, more consistent toner product quality since there is no or little batch to batch variation as is encountered in the batch process, smaller size equipment such as 2 to 4 times smaller than the prior art batch process can be used, and additional process variables such as flow rate, method of feeding, and recirculation rate can be readily selected for control of product quality.
Encapsulated toners and processes thereof, such as batch processes, are known as indicated herein. For example, both U.S. Pat. No. 4,626,489 and British Patent 1,538,787 disclose similar processes for colored encapsulated toners wherein both the core resin and shell materials are prepared by free radical polymerization techniques. U.S. Pat. No. 4,565,764 discloses a colored microcapsule toner comprised of a colored core encapsulated by two resin shells with the inner shell having an affinity for both the core and the outer shell materials; and U.S. Pat. No. 4,254,201 illustrates the use of pressure sensitive toner clusters or aggregates with each granule of the cluster or aggregate being comprised of a pressure sensitive adhesive substance encapsulated by coating film. Color pigment particles or magnetic particles can be present on the surfaces of the encapsulated granules to impart the desired color to the toners. Also, U.S. Pat. No. 4,727,011 discloses a process for preparing encapsulated toners which involves a batch shell forming interfacial polycondensation and a core binder forming free radical polymerization, and further U.S. Pat. No. 4,708,924 discloses the use of a mixture of two polymers, one having a glass transition temperature in the range of -90.degree. C. to 5.degree. C., and the other having a softening temperature in the range of 25.degree. C. to 180.degree. C., as core binders for a pressure fixable encapsulated toner. Other prior art, all U.S. patents, include: U.S. Pat. No. 4,016,099, which discloses methods of forming encapsulated toner particles and wherein there are selected organic polymers including homopolymers and copolymers, such as vinylidene fluoride, tetrafluoroethylene, chlorotrifluoroethylene, and the like, see column 6, beginning at line 3, wherein there can be selected as the core materials polyolefins, polytetrafluoroethylene, polyethylene oxide and the like, see column 3, beginning at around line 18; U.S. Pat. No. 4,265,994 directed to pressure fixable capsule toners with polyolefins, such as polytetrafluoroethylene, see for example column 3, beginning at line 15; U.S. Pat. No. 4,497,885, which discloses a pressure fixable microcapsule toner comprising a pressure fixable component, a magnetic material, and other optional components, and wherein the core material can contain a soft material typical examples of which include polyvinylidenefluoride, polybutadiene, and the like, see column 3, beginning at line 10; U.S. Pat. No. 4,520,091 which discloses an encapsulated toner with a core which comprises a colorant, a dissolving solvent, a nondissolving liquid and a polymer, and may include additives such as fluorine containing resin, see column 10, beginning at line 27; U.S. Pat. No. 4,590,142 relating to capsule toners wherein additives such as polytetrafluoroethylenes are selected as lubricating components, see column 5, beginning at line 52; U.S. Pat. Nos. 4,599,289 and 4,803,144. The aforementioned prior art is believed to be silent with respect to the preparation of encapsulated toners by a continuous process as illustrated herein.
With further specific reference to the prior art, there are disclosed in U.S. Pat. No. 4,307,169 microcapsular electrostatic marking particles containing a pressure fixable core, and an encapsulating substance comprised of a pressure rupturable shell, wherein the shell is formed by an interfacial polymerization. One shell prepared in accordance with the teachings of this patent is a polyamide obtained by interfacial polymerization. Furthermore, there are disclosed in U.S. Pat. No. 4,407,922 pressure sensitive toner compositions comprised of a blend of two immiscible polymers selected from the group consisting of certain polymers as a hard component, and polyoctyldecylvinylether-co-maleic anhydride as a soft component. Interfacial polymerization processes are selected for the preparation of the toners of this patent.
In a patentability search report, references cited therein, all U.S. Patents and indicated as being only of collateral interest, include U.S. Pat. Nos. 5,071,451; 4,727,011; 4,851,318; 4,537,167; 4,954,412; 5,035,970 and 5,037,716.
The disclosures of all the United States patents and other patent documents mentioned herein are totally incorporated herein by reference.
A number of patents illustrate various encapsulated toner compositions and batch processes for the preparation thereof including, for example, U.S. Pat. No. 5,043,240 , U.S. Pat. No. 5,035,970, U.S. Pat. No. 5,037,716, U.S. Pat. No. 5,045,428, U.S. Pat. No. 5,023,159 and U.S. Pat. No. 5,013,630, the disclosures of each of the aforementioned patents being totally incorporated herein by reference.
Generally, the known batch encapsulated toner processes involve dispersion in a vessel for an effective period of time of an oil phase comprised of a pigment, one or two core monomers and an oil soluble shell monomer in an aqueous solution containing a small fraction of surfactant using a rotor-stator homogenizer; thereafter transferring the resulting suspension to a batch reactor vessel equipped with a mechanical stirrer, subsequently adding to the batch reactor a water soluble monomer such as an amine, and effecting interfacial polymerization of the amine and oil soluble shell monomer such as isocyanate to form a polymeric shell, and then effecting free radical polymerization by heating of the core monomer at a temperature of from about 75.degree. to 95.degree. C.
Disadvantages associated with the aforementioned batch processes for the preparation of encapsulated toners include long processing times, from 8 to 15 hours for example, because of the times needed to charge the materials, transfer the materials from one vessel to another and discharge them, low volume/time yield, such as 2 to 4 times lower than that achieved by the continuous processes of the present invention in embodiments, of toner due to the long processing time and shutdown time which is needed for charging and discharging of materials and cleaning of the equipment; laborious apparatus changeover operations such as the transfer of a suspension from a particle formation mixing tank to a reactor and periodic addition of materials such as addition of amine to induce interfacial polymerization; shutdown of the operation after each toner run to discharge the material and clean the reactor; and batch to batch variation in the toner quality obtained due to preparation of a different batch by a different operator.
Disclosed in copending patent application U.S. Ser. No. 617,234 is the preparation of encapsulated toners by a batch process which comprises (1) dispersing a mixture of one or more core monomers, an oil-soluble free radical initiator or initiators, at least one oil-soluble shell precursor or monomer component, colorants, an optional preformed core resin, such as a styrene polymer, an acrylate polymer, a methacrylate polymer, a polyester, and the like present in an effective amount of, for example, from about 0 to about 50 weight percent of the total core polymers, and an optional diluent, by high shear blending into stabilized microdroplets having a specific droplet size and size distribution in an aqueous medium containing a surfactant or stabilizer; (2) initiating the shell-forming interfacial polycondensation by adding one or more water-soluble shell precursors or monomer components; (3) thereafter, effecting the core resin-forming free radical polymerization by heating, leading to the formation of encapsulated toner particles; and (4) treating the resulting encapsulated particles with a silane reagent. The core resin-forming free radical polymerization is generally conducted in a temperature range of from about 35.degree. C. to over about 120.degree. C., and preferably from about 45.degree. C. to about 90.degree. C., for a period of from about 1 to about 24 hours, depending primarily on the monomers and free radical initiators used.